If the resolution of an imaging device is comparable to the size of the object being imaged, so called "partial volume" effects occur, which distort the intensity of the image. This is the situation when PET or SPECT devices (typically 6-16 mm resolution) are used to image the heart wall (typically 4-14 mm thick). This partial volume effect distorts the apparent uptake of radioisotope in the heart, potentially confounding diagnostic interpretation. An investigation was made into the various factors which produce this effect (cardiac motion, imaging resolution characteristics, wall thickening, etc.). Simulations were used to determine the magnitude by which each of the effects might distort clinical images in an effort to determine optimal imaging characteristics for diagnostic use. In addition, a study is underway to determine if the usually deleterious partial volume effects could be used to advantage to estimate cardiac thickening, by using the artefactual change in apparent image intensity from end diastole to end systole. This method is being compared to other reported methods, based on mathematical fitting functions, to determine which might be the optimum method to use m clinical practice. The first portion of this study is complete and has been recently published. The comparison of methods part of the study is now complete and is being submitted for publication. This study led to the development of a new method for measuring thickening, which is under study in ZOI-CL-0041 1-01.